How to evaluate site content with sitemap?

Google shows 25% of sitemap indexed. I would like to figure out why.

[mrjohncory]

I just read this post and would respond there but it's too old:
[webmasterworld.com...]

I have a site where Google shows the following for our URLs in sitemap:

Total: 2,069, Indexed: 593

This number has been steadily declining for 3 months, perhaps longer. (I started working on the site 3 months ago.)

I can understand that Google may not want to index everything on the site but how would I...

1) most easily go about determining which 1476 pages are not being indexed

2) group those pages for review/analysis

[gwnhwyvar]

Wish I had an answer but I'm having the same problem and can't figure it out, either. Misery does love company but sadly that doesn't fix the problem does it! :(

[anallawalla]

What is the count with the site: operator in Google Search? Since you have only 593 pages indexed, you could view all/most of them with this operator. Test their ranking by searching for an obvious keyphrase that is prominent on them.

The rest are not indexed.